Secondary cell having a lithium intercolating manganese oxide

ABSTRACT

A secondary lithium ion cell having an anode, a cathode and a nonaqueous electrolyte wherein the cathode comprises sub-micron-size amorphous, microporous, lithium-intercalateable manganese oxide having an internal surface area greater than about 100 m 2  /g. The cathode may include an electrically conductive lithium-intercalateable polymer binder. A sol-gel process for making the amorphous quatravalent manganese oxide is disclosed.

This invention relates to secondary, lithium-ion cells having amorphous,quatravalent, Li-intercalateable manganese oxide cathodes, and a methodof making same.

BACKGROUND OF THE INVENTION

Secondary, lithium-ion cells and batteries are well known in the art.One such lithium-ion cell comprises essentially alithium-intercalateable carbonaceous anode, a lithium-intercalateable,chalcogenide cathode, and a non-aqueous, lithium-ion-conductingelectrolyte therebetween. The carbon anode comprises any of the variousforms of carbon (e.g., coke or graphite fibers) pressed into a porousconductor or bonded to an electrically conductive carrier (e.g. copperfoil) by means of a suitable organic binder. A known chalcogenidecathode comprises a crystalline spinel form of manganese oxide bonded toan electrically conductive carrier (e.g., aluminum foil) by a suitableorganic binder such as ethylene propylene diene monomer (EPDM).

Lithium-ion cell electrolytes comprise a lithium salt dissolved in avehicle which may be (1) completely liquid, or (2) an immobilizedliquid, (e.g., gelled, or entrapped in a polymer matrix), or (3) a purepolymer. Known polymer matrices for entrapping the electrolyte includepolyacrylates, polyurethanes, polydialkylsiloxanes, polymethacrylates,polyphosphazenes, polyethers, and polycarbonates, and may be polymerizedin situ in the presence of the electrolyte to trap the electrolytetherein as the polymerization occurs. Known polymers for pure polymerelectrolyte systems include polyethylene oxide (PEO),polymethylene-polyethylene oxide (MPEO) or polyphosphazenes (PPE). Knownlithium salts for this purpose include, for example, LiPF₆, LiClO₄,LiSCN, LiAlCl₄, LiBF₄, LiN(CF₃ SO₂)₂, LiCF₃ SO₃, LiC(SO₂ CF₃)₃, LiO₃SCF₂ CF₃, LiC₆ F₅ SO₃, and LiO₂ CF₃, LiAsF₆, and LiSbF₆. Known organicsolvents (i.e., vehicles) for the lithium salts include, for example,propylene carbonate, ethylene carbonate, dialkyl carbonates, cyclicethers, cyclic esters, glymes, lactones, formates, esters, sulfones,nitriles, and oxazolidinones.

Lithium cells made from pure polymer electrolytes, or liquidelectrolytes entrapped in a polymer matrix, are known in the art as"lithium-polymer" cells, and the electrolytes therefor are known aspolymeric electrolytes. Lithium-polymer cells are often made bylaminating thin films of the anode, cathode and electrolyte togetherwherein the electrolyte layer is sandwiched between the anode andcathode layers to form an individual cell, and a plurality of such cellsare bundled together to form a higher energy/voltage battery. In makingsuch cells, it is desirable that the thin films be flexible and robustso that they can be handled without damage.

While electrodes made from manganese oxide spinels are relativelyinexpensive, and produce cells having a desirable high dischargeterminal voltage (i.e., 4 volts), they are not without problems. Forexample, electrodes made therefrom have poor conductivity and requirethe addition of conductive fillers (e.g., carbon) to enhanceconductivity. The addition of such fillers reduces the energy density ofthe electrode. Moreover, recharging cells requires impressing a voltagethereon which exceeds the discharge terminal voltage of the cell. Hencefor cells having manganese oxide spinel cathodes, it takes at least 4.1volts (and preferably more) to intercalate lithium from the electrodeduring charging of the cell. Above about 4.5 volts, however, thesolvents for the electrolyte oxidize and decompose. Hence, it isnecessary to carefully control the charging voltage of such cells belowthe decomposition potential of the solvent in order to preventdegradation thereof. Furthermore, due to the crystalline structure ofspinel manganese oxide, their reversible capacity and cycle life aresensitive to overcharge and overdischarge. Discharge of manganese oxidespinel cells must be cut-off when the terminal voltage falls to about3.4 volts. This limits the capacity of the material which typicallypeaks at about 140 mAh/g. Below about 3.4 volts, the spinel form of themanganese oxide undergoes structural transformation when additionallithium is inserted into LiMn₂ O₄ and it converts to the orthorhombicform which has very poor cycleability, and is very unstable causing theformation of other manganese oxides which are not electrochemicallyactive. Still further, insertion of more than one lithium into spinelmanganese oxide results in cation mixing between octahedral andtetrahedral sites which leads to continuous capacity decay. To avoidthese problems, the cell voltage must be controlled electronicallyduring the operation of the cell. Such control is very difficult tomanage when a number of large lithium cells are coupled together inseries. Finally, spinel-type manganese oxide electrodes typically haveinternal surface areas less than about 40 m² /g, which limit theirintercalation capacity and the rate at which they can be discharged andrecharged.

SUMMARY OF THE INVENTION

The present invention contemplates a relatively voltage-insensitivemanganese oxide electrode for a lithium-ion cell which, compared tospinel manganese oxide electrodes, has (1) a much higher dischargecapacity (i.e., as high as 240 mAh/g) and internal surface area (i.e.,as high as ca 380 m² /g), and (2) a much lower recharge voltage (i.e.,ca. 4 volts) and discharge cut-off voltage (i.e., ca. 2.0 volts).Preferred electrodes according to the present invention include anactive material comprising amorphous, microporous, quatravalent,submicron-sized, manganese oxide particles formed by a sol-gel processand having an internal surface area greater than 100 m² /g. A mostpreferred such active material has the 2 quatravalent manganese oxideparticles mixed with an electrically conductive, lithium-intercalateablepolymer (e.g., polyaniline or its derivatives) polymerized in situ withthe formation of the quatravalent manganese oxide. Electrodes made fromsuch polymers may supplement or replace inert binders, and inertconductive diluents, used heretofore to form electrodes, and therebyincrease the capacity of the electrodes. Other conventional binders mayalso be used in combination with the intercalateable polymer.

The amorphous, manganese oxide of the present invention is made by: (1)dissolving a first manganese compound having a manganese oxidation state(i.e., valence) greater than 4 in a first polar solvent (e.g., water) toform a first solution; (2) dissolving a second manganese compound havinga manganese oxidation state less than 4 in a second polar solvent (e.g.,water) to provide a second solution; (3) dispersing the second solutionrapidly throughout the first solution until substantially all of thefirst compound is reduced and forms a gel containing said quatravalentmanganese oxide; and (4) drying the gel to recover the quatravalentmanganese oxide therefrom as submicron-size particles. Electrodes aremade therefrom by mixing the manganese oxide with a binder and applyingit to a suitable conductive substrate. To achieve large internal surfaceareas for the quatravalent manganese oxide, the first solution willpreferably have a pH less than 7, more preferably less than 5, and mostpreferably less than about 2. The first manganese compound willpreferably comprise a permanganate ion, and the second manganesecompound will preferably comprise a manganous salt. Most preferably, thesecond solution will also contain a liquid, oxidatively polymerizeablepolymer precursor (e.g., monomer, or short chain polymer) for forming anelectrically conductive, lithium intercalateable polymer binder in situthroughout the amorphous manganese oxide at the molecular level with theconductive polymer apparently being inserted between molecules ofmanganese oxide. Such intermolecular insertion enhances electricalconductivity to an extent not seen possible by mere mechanical mixing ofthe components.

DETAILED DESCRIPTION OF THE INVENTION

The invention will better be understood when considered in the light ofthe following description of certain specific embodiments thereof whichis given hereafter in connection with the several Figures in which:

FIG. 1 is a plot of the internal surface area of the amorphous manganeseoxide of the present invention as a function of the particle sizethereof;

FIG. 2 is a plot of the effects of pH on the internal surface area ofthe amorphous manganese oxide;

FIG. 3 is a plot of the electrical conductivity of the amorphousmanganese oxide as a function of the concentration of polyanalinetherein;

FIG. 4 is a scanning electron microscope (SEM) photo (i.e., at 50 Kmagnification) of the amorphous manganese oxide of the presentinvention;

FIG. 5 is an X-ray diffraction pattern of the amorphous manganese oxideof the present invention;

FIG. 6 shows the voltage profiles of an electrode made from theamorphous manganese oxide of the present invention at different stagesduring charge-discharge cycling;

FIG. 7 is a plot of the cycling efficiency of an electrode made from theamorphous manganese oxide of the present invention over a number ofcycles; and

FIG. 8 are plots of the discharge capacities of spinel manganese oxideand the amorphous manganese oxide of the present invention over a numberof cycles.

In accordance with the present invention, there is provided a cathodefor a lithium-ion cell comprising amorphous, microporous,lithium-intercalateable, quatravalent, submicron-size, manganese oxideparticles having an internal surface area greater than about 100 m² /g.The amorphous, quatravalent manganese oxide particles of the presentinvention are made by a sol-gel process wherein a first solution of amanganese compound having a manganese oxidation state greater than 4(Mn^(hi)) is mixed with a second solution of a second manganese compoundhaving a manganese oxidation state less than 4 (Mn^(lo)). The higheroxidation state manganese is reduced and the lower oxidation statemanganese is oxidized to form a gel containing quatravalent manganeseoxide. The second solution is slowly (preferably, incrementally as by aseries of droplets) added and rapidly admixed with the first solution soas to rapidly disperse the second solution throughout the firstsolution, and thereby form submicron-sized particles of amorphousquatravalent manganese oxide having an internal surface much greaterthan 40 m² /g and preferably between about 100 m² /g and about 380 m²/g. By way of contrast, crystalline spinel-type manganese oxides must beground to produce small particles, and typically have internal surfaceareas less than about 40 m² /g. Electrodes made from amorphous manganeseoxide have demonstrated capacities greater than about 200 mAh/g in sharpcontrast to 140 mAh/g capacity obtained from spinel-type manganeseoxide.

The first solution comprises a first manganese compound having amanganese oxidation state greater than 4 and may include such manganesecompounds as alkaline permanganates (e.g., sodium permanganate) andalkaline manganates (e.g., potassium manganate). Compounds containingpermanganate ions (i.e., Mn⁺⁷) are preferred, with the alkali metalpermanganates being most preferred for their ready availability andsolubility in polar solvents. Suitable polar solvents for this purposeinclude water, cyclic carbonates, linear carbonates, cyclic esters andcyclic ethers. Water is the most preferred polar solvent as it is theleast expensive, most readily available and can dissolve as much as 0.5moles of sodium permanganate at room temperature.

The second solution will comprise having an manganese compound(s) havingan oxidation state less than 4, e.g., manganese sulfate, manganesenitrate and manganese acetate. The manganous salts, and particularlymanganese nitrate, are most preferred owing to their ready availability,and solubility in polar solvents (preferably water) such as mentionedabove for the first solution. The second solution is slowly added (i.e.,in small increments/droplets) to the first solution, and rapidlydispersed throughout the first solution to insure the formation of thesmallest quatravalent, manganese oxide particles possible upon drying ofthe gelatinous reaction product formed. In this regard, the first andsecond solutions react to form a gel which contains the quatravalentmanganese oxide, and which, upon drying/dehydration, gives up thequatravalent manganese oxide in the form of amorphous, high surfacearea, submicron-sized particles (i.e., typically having diameters lessthan about 0.3 microns) without the need for any significant grinding orpulverization as is typically required to obtain small particles ofspinel manganese oxides. Reduction of the high oxidation state manganesewith the low oxidation state manganese and consequent oxidation of thelow oxidation state manganese results in the formation of very uniform,quatravalent, manganese oxide which is both amorphous and has anunexpectedly high internal surface area.

Dilute first and second solutions provide the smallest particles which,in turn, correlates to high internal surface areas. Hence, for example,a first solution comprising sodium permanganate having a sodiumpermanganate concentration less than about 0.3 molar will preferably bereacted with a second solution having a manganous ion (e.g., manganousnitrate) concentration equal to or less than the permanganateconcentration. It is desirable to consume all of the permanganate in thereaction because any unreacted permanganate becomes trapped in the poresof the quatravalent manganese oxide, and breaks down upon heating.Excess manganous ion, on the other hand, can readily be washed away fromthe quatravalent manganese oxide particles, and hence may be used inexcess in order to insure complete reaction of the permanganate.Ideally, however, stoichiometric amounts of permanganate and manganousion will be used so that there is no need to have to deal with anyunreacted high or low oxidation state manganese in the residue followingdrying. In the case of the permanganate solution, it is easy todetermine when the permanganate is completely consumed as thepermanganate solution starts out as a dark reddish purple color butprogressively lightens and losses its color as the manganous ion isadded and the permanganate is reduced to quatravalent manganese. Whenthe color completely disappears, the reaction is complete and noadditional manganous ion addition is required.

Rapid stirring or mechanical agitation of the first solution isdesirable as the second solution is being slowly added thereto.Agitation or rapid stirring of the first solution insures that thesecond solution is rapidly mixed and dispersed throughout the firstsolution as it is slowly added thereto in order to insure the formationof submicron sized particles of the quatravalent manganese oxide. Whilerapid stirring the first solution is a particularly convenient way tointimately mix the solutions together, rapid mixing may also be achievedby injecting or spraying the second solution into a stream of the firstsolution. Other rapid mixing techniques known to those skilled in theart may also be employed with the goal being to disperse the secondsolution reactants throughout the first solution before any significantreaction occurs and thereby form submicron size, highly porousquatravalent manganese oxide particles upon drying of the gel formed.

The reaction between the first and second solutions forms a single phasegel containing the quatravalent manganese oxide. The gel is dried toremove the solvent and recover amorphous manganese oxide particles.Hence where water is the solvent, the gel is dewatered and dehydrated.Dewatering of the gel is conveniently accomplished by vacuum filteringthe gel to remove much of the water followed by washing the filtratewith distilled water and then heating it (i.e., 100° C.-180° C.) undervacuum to completely dry out the gel and leave a residue ofquatravalent, amorphous manganese oxide particles in its stead.

Depending on the conditions used in the sol-gel process, amorphous,quatravalent manganese oxide particles as small as 0.01 microns havebeen produced having internal surface areas as high as about 380 m² /g.Other conditions have produced particle sizes as large as 0.3 micronshaving internal surface areas of about 200 m² /g. As a general rule, theinternal surface area of the particles varies with the size of theparticles. In this regard, FIG. 1 qualitatively illustrates that theinternal surface area of the particles increases as the particle sizedecreases. The trend line of FIG. 1 is based on a subjective analysis ofSEM photos of particles and surface area measurements of such particles.Quatravalent manganese oxide particles made in accordance with thepresent invention will preferably have particle sizes less than about0.3 microns and internal surface areas greater than about 200 m² /g,though it is recognized that particles having larger particle size andlower internal surface areas (i.e., above about 100 m² /g) may beproduced which are still superior to spinel-type manganese oxides usedheretofore.

The Mn^(hi) -Mn^(lo) oxidation reduction reaction of the presentinvention will preferably take place in an acidic environment. To thisend, the first solution will preferably have a pH less than 7, morepreferably less than 5 and most preferably less than about 2. The acidicenvironment discourages the formation of undesirable oxides such as Mn₂O₃, MnO, and MnOOH, and promotes the formation of amorphous manganeseoxide having very high internal surface areas. Such high surface areamaterials have greater current-producing capacity as measured inmilliampere hours per gram (mAh/g) of manganese oxide. In this regard,FIG. 2 shows that as the acidity of the reaction environment increases(i.e., the pH decreases) the internal surface area of the amorphousquatravalent manganese oxide increases with the best result beingachieved when the pH is below about 2. Excellent results have beenobtained at a pH as low as -1. pH is preferably controlled with the useof oxidizing acids such as HClO₄ or H₃ PO₄ which further promote theformation of stable Mn⁺⁴. Internal surface area determinations were madeusing Autosorb I equipment from Quanta Chrome Corp. to take BETmeasurements. This equipment utilizes a static volumetric method tomeasure the quantity of gas adsorbed or desorbed from a solid surface atsome equilibrium vapor pressure. The samples were first outgased at 150°C. for at least 8 hours then cooled down by liquid nitrogen for theadsorption measurements made with nitrogen gas. Pressure charges in theequipment were measured during gas adsorption and desorption and thevalues used to calculate the surface area.

Preferably, the first solution containing the high oxidation statemanganese will be heated to further insure the formation of the moredesirable ultra small particles. Heating will preferably be in the rangeof about 60° C. to about 85° C.

The solvent for both solutions will preferably comprise water, butvirtually any polar solvent for the high and low oxidation statemanganese compounds will be effective to various degrees. Hence forexample, amorphous, quatravalent manganese oxide has been made inaccordance with the present invention using propylene carbonate as asolvent for both the permanganate and manganous ions. However, the useof organic solvents slows the process and adds to the cost andcomplexity thereof without appearing to add any particular advantagethereto. For example compared to water, it is more difficult to removepropylene carbonate solvent from the gel after the gelling reaction iscomplete. On the other hand, there may be advantages to using differentsolvents for the two solutions in order to control particle size. Henceusing water as the solvent for the first solution and propylenecarbonate, or another organic solvent, as the solvent for the secondsolution may permit better dispersion of the manganous solutionthroughout the first solution before significant reaction with thepermanganate occurs resulting in smaller particles than might otherwisebe possible under the same conditions of temperature, concentration andacidity.

Electrodes are made by mixing the amorphous quatravalent manganese oxideparticles of the present invention with a suitable binder (e.g., EPDM)in a solvent, coating the mix onto a suitable electrically conductivesupport (i.e., aluminum foil) and removing the solvent (e.g., as byheat) to adhere the manganese oxide to the support, as is well known inthe art. Coating may be effected by spraying, spin-coating,blade-coating, electrostatic spraying, painting, etc. Some conductivecarbon particles may be mixed with the manganese oxide to improve itselectrical conductivity as is also well known in the art. Suchelectrodes will typically comprise about 3% to about 10%, by weight,binder, and about 5% to about 15%, by weight, conductive carbonparticles.

In accordance with a most preferred embodiment of the present invention,a lithium-intercalateable and electrically conductive polymer is formedin situ during the oxidation-reduction reaction that forms thequatravalent, manganese oxide. Such a polymer not only enhances theelectrical conductivity of the amorphous manganese oxide activematerial, but function at least partly, if not totally, as a binder forthe manganese oxide material which increases the lithium intercalationcapacity of electrodes made therefrom as compared to electrodes madeentirely from inert binders. Hence, the polymers of the most preferredembodiment perform three functions to-wit: (1) binder, (2) conductivityenhancer, and (3) Li-intercalation capacity enhancer. By adjusting theamount of such polymer in the manganese oxide active material, it ispossible to adjust (1) the electrical conductivity of the activematerial, and (2) the flexibility/durability of films formed therefrom.Use of such polymers reduces the amount of inert carbon particlesotherwise needed to provide conductivity. Hence whereas without suchpolymer the carbon particle loading would typically be about 10%-15% byweight, with the conductive polymer the carbon loading can be reduced toabout 5% with a corresponding increase in capacity owing to theLi-intercalateability of the polymer. Similarly, such a polymer can alsoreplace much or all of the ineert binder typically used heretofore witha corresponding increase in capacity. As the electrically conductive,Li-intercalateable polymer has less intercalateable capacity (e.g., ca100 mAh/g for polyaniline) then the amorphous, quatravalent manganeseoxide, the concentration of the polymer should be kept to a minimumconsistent with the electrical conductivity and flexibility/durabilityrequirements of electrodes made therefrom. In other words, as thepolymer concentration increases the conductivity, flexibility anddurability of the electrode increases, but at some sacrifice to thelithium intercalateability of the electrode. The concentration of theconductive polymer binder in the manganese oxide mix will generally beabout 10% to about 20% by weight. A preferred conductive/intercalateablepolymer comprises polyaniline or its derivatives (e.g., alkylpolyanilines) produced by the in situ oxidation of precursors thereof(e.g., aniline monomer or short chain aniline polymer). A number ofother polymers known to be conductive, intercalateable and capable ofbeing polymerized by oxidation by the permanganate ion includespolythiophene, polypyrrole and their derivatives, and are also seen tobe effective binders. Corresponding liquid monomer or short chainpolymer precursers having at least one repeating unit will be added tothe reaction mix. In accordance with the preferred embodiment, theconcentration of the aniline precursers in the second solution (i.e.,Mn^(lo)) will vary from about 5 mol percent to about 30 mol percentrelative to the manganous ion concentration therein. The oxidation powerof the Mn^(hi) solution is sufficient to polymerize the aniline monomerto polyaniline when aniline (a reducing agent) is present. Theconcentration of the Mn^(lo) in the second solution can be reduced bythe amount of reducing power provided by the presence of anilinetherein. By way of example, the stoichiometry of manganous, manganateand aniline can be obtained from:

m[Mn⁷ +3e →Mn⁴ ]

n[Mn² →Mn⁴ +2e]

p[aniline→polyaniline+e]

yielding a net reaction:

m[Mn⁷ ]+n[Mn² ]+p[aniline]→(m+n)Mn⁴ ·aniline_(p) where 3m=2n+p and n andp are variables that can be adjusted to control capacity, electricalconductivity and mechanical flexibility of the electrode material.

To function as a binder the electrically conductive, lithiumintercalateable binder must be coalesced. This can be effected by hotpressing or by mixing the polymer-MnO₂ composite with a solvent for thepolymer followed by removing (e.g., evaporating) the solvent.Polyaniline, for example, can be fused together at about 250° C. ordissolved in such solvents as doocylbenzene sulfonic acid,decahydronaphthalene, or their derivatives. Any heating of the compositematerial should be kept below about 400° C. to prevent crystallizationof manganese oxide.

TESTS

Example 1--a batch of amorphous, quatravalent manganese oxide was madeby: (1) preparing one (1) liter of a first aqueous solution comprising0.25 mole of sodium permanganate and adjusting its pH to 1 with HClO₄ ;(2) preparing a second aqueous solution comprising 0.35 moles ofmanganese nitrate in 1 liter; (3) heating the first solution to atemperature of 80° C. while mechanically agitating it; (4) adding 1liter of the second solution to the first solution as a series ofsuccessive droplets until the mix gelled and the purplish color of thefirst solution disappeared; (5) filtering the gel under a vacuum of 10⁻³Torr; (6) rinsing the filtrate with distilled water; and (7) drying thefiltrate at 180° C. under a 10⁻³ Torr vacuum for eight (8) hours. Thematerial thusly made was subjected to X-ray diffraction analysis. TheX-ray diffraction pattern is shown in FIG. 5. The pattern shows theamorphous character of the manganese oxide produced with the peaks at 32and 56 (two theta) being attributed to the sample holder. A scanningelectron microscope photograph of this material is shown in FIG. 4.

Example 2--a number of samples were made as set forth in Example 1 withvarying concentrations of polyaniline conductive polymer present in thefinished product. The electrical conductivity of the various samples wasmeasured and plotted in FIG. 3 as a function of polyanilineconcentration. The plot shows that as polyaniline concentrationincreases the conductivity of the composite increases.

Example 3--Electrodes were made from the materials described in Example2 by mixing varying amounts (i.e., 0 to 20% by weight) of conductive KS2graphite powder therewith in inverse proportion to the concentration ofthe conductive polymer (i.e., polyaniline) therein. These mixes werefurther mixed with a solution comprising 4% by weight EPDM in a 50:50volume ratio of cyclohexan and xylene and mechanically mixed for from 2to 4 hours to form a slurry. The slurry was coated onto either analuminum foil or a carbon-coated aluminum foil current collector forfurther tests and the coated current collector subjected to a vacuum of10⁻³ Torr at a temperature of 100° C. for one (1) hour to remove any ofthe cyclohexan and xylene solvents that had not already evaporated. Testcells were made with the electrodes so made using lithium foil as ananode, and an electrolyte comprising either a one (1) molar solution oflithium perchlorate in propylene carbonate, or an one (1) molar solutionof LiPF₆ in a 50:50 mixture of ethylene carbonate/dimethyl carbonate. Acopper disk contacted the anode and an aluminum disk contacted themanganese oxide electrode to carry the cell current. Charge-dischargecycling of the cell was conducted using constant currents varying from0.2 to 2 mA/cm² over a series of several tests. A Maccor battery cyclerwith a PC386 computer was used to cycle the cells and collect data. FIG.6 shows voltage profiles for one such manganese oxide cathode cycled ata current density of 0.5 MA/Cm² between 2.5 volts and 4.2 volts. Curve 1shows the voltage profile for the first full cycle. Curve 10 shows thevoltage profile for the 10th cycle. Curve 20 shows the voltage profilefor the 20th cycle. Curve 30 shows the voltage profile for the 30thcycle. The voltage profile maintains continuous gradients between thelimiting voltages which is characteristic of amorphous materials.Moreover as the plot shows, most of the reversible capacity is below 4volts where the electrolyte and electrode are stable. This is contrastedwith spinel phase manganese oxide electrodes where most of thereversible capacity resides in a narrow high-voltage band between 4.0and 4.2 volts (i.e. vs. lithium) and close to the decompositionpotential of the electrolyte. Moreover, FIG. 6 also shows the cyclingperformance of the manganese oxide cathode. The symmetriccharge-discharge curves indicate reversible and efficient performance ofthe cathode. FIG. 7 shows the charge-discharge-cycling efficiency of thecathode cycled in FIG. 6 and shows a near 100% cycling efficiency.Finally, FIG. 8 shows the discharge capacity (i.e., milliampere hoursper gram) of amorphous manganese oxide of the present invention (curveA) compared to the discharge capacity of a spinel LiMn₂ O₄ electrodecycled at the same current density in the same electrolyte.

Example 4--A number of samples were prepared with various amounts ofpolyaniline polymer therein (i.e., as a binder and conductive diluentsubstitute) to determine the affects of the polyaniline on theelectrode's capacity (i.e., lithium intercalateability). A firstsolution (i.e., solution A) was prepared comprising 0.25 molar sodiumpermanganate acidified by HClO₄ to pH=1. A second solution (i.e.,solution B) was prepared comprising 0.375 molar manganese nitrate.Various amount of aniline monomer was added to different amounts ofsolution B. This solution was blended to uniformly disperse the anilinein the manganese nitrate solution using a high speed blender. The mixedsolution was added dropwise to, and rapidly stirred into 1000 ml ofsolution A maintained at 80° C. The exothermic reactions between the twosolutions occurred and a uniform gel was formed that filled a volume ofabout 2000 ml. The gel was filtered under a vacuum of 10⁻³ Torr. Thefiltered gel was dried in a vacuum oven (10⁻³ Torr) at 180° C. for about4 hours. The dried gel powder was used as active material for making abattery electrode. A battery electrode was made from 2 grams of the gelpowder. EPDM binder was first dissolved in a 50/50 cyclohexane/xylenesolvent to make a 2% EPDM solution. KS-2 graphite powder was added as aconductive diluent. The amount of conductive KS-2 powder was adjustedaccording to the concentration of polyaniline in the metal oxide. Theamount of polyaniline, manganese oxide powder, EPDM binder, and KS-2used to make the test electrodes are listed in Table 1 for seven (7)samples including an aniline-free reference sample. The mixture ofpolyaniline, manganese oxide, EPDM binder, and diluent graphite powderwas micronized for 15 minutes in an agate-ball type micronizing millsold by McCrone to form a slurry with a thick-ink viscosity, and spreadover an aluminum foil using a doctor blade technique. The coating wasdried in air for 1 hour then further dried under a vacuum of 10⁻³ Torrat 100° C. for more than 1 hour. A disk electrode (diameter 2.54 cm) waspunched out from the coating and used in an electrochemical cell havingmetallic lithium as a counter electrode, and 1M LiClO4 in ethylenecarbonate/dimethyl carbonate (50/50 mole ratio) as the electrolyte. AMaccor battery cycler was used to cycle the cell between 2.0-4.3 voltsat 0.2 mA/cm². Capacity of the active material in the electrodes wasmeasured (mAh), normalized per its weight (mAh/g) and shown in Table 1for each test sample. Table 1 also shows the polyaniline, MnO_(x), EPDMand KS-2 content of each sample. These tests show that samples 1-4 whichhad MnO_(x) /polyaniline ratios between about 95/5 to 80/20 EPDM levelsas low as 2% and KS-2 levels as low as 2% had higher capacities than thepolyaniline-free reference electrode and electrodes (samples 5 & 6)having higher polyaniline content.

                                      TABLE 1                                     __________________________________________________________________________    composition and capacity of various composite electrode.                      B      Aniline                                                                           MnO.sub.x /                                                                         EPDM binder                                                                           KS-2                                                                              MnO.sub.x + PA                                                                       Electrode Capacity                        (ml)   (ml)                                                                              Polyaniline                                                                         (wt %)  (wt %)                                                                            (wt %) (mAh/g)                                   __________________________________________________________________________    Ref                                                                              1000                                                                              0   00% MnO.sub.x                                                                       5       10  85     196.4                                     1  917 5.63                                                                              95/5  2       7   91     203.38                                    2  834 11.25                                                                             90/10 2       5   93     200.18                                    3  751 16.87                                                                             85/15 2       3   95     198.23                                    4  668 22.50                                                                             80/20 2       2   96     198.02                                    5  585 28.13                                                                             75/25 2       2   96     186.17                                    6  502 33.76                                                                             70/30 2       2   96     181.34                                    __________________________________________________________________________

While the invention has been disclosed in terms of certain specificembodiments thereof it is not intended to be limited thereto, but ratheronly to the extent set forth hereafter in the claims which follow.

What is claimed is:
 1. In a secondary lithium-ion cell comprising ananode, a cathode and a non-aqueous, lithium-ion conducting electrolytebetween said anode and cathode, the improvement wherein said cathodecomprises submicron-size, amorphous, microporous,lithium-intercalateable, quatravalent, manganese oxide particlessupported on an electrical conductor, said particles having an internalsurface area greater than about 100 m² /g.
 2. A cell according to claim1 wherein said manganese oxide has a particle size less than about 0.3microns and an internal surface area greater than about 200 m² /g.
 3. Ina secondary lithium-ion cell comprising an anode, a cathode and anon-aqueous, lithium-ion conducting electrolyte between said anode andcathode, the improvement wherein said cathode comprises submicron-size,amorphous, microporous, lithium-intercalateable, quatravalent, manganeseoxide particles supported on an electrical conductor and bound togetherby an electrically conductive, lithium-intercalateable, polymer, saidparticles having an internal surface area greater than about 100 m² /g.4. A secondary cell according to claim 3 wherein said polymer isselected from the group consisting of polyaniline, polypyrole,polythiophene and derivatives thereof.
 5. A secondary cell according toclaim 4 wherein said polymer comprises polyaniline.
 6. A secondary cellaccording to claim 5 wherein said polyaniline comprises up to about 22%by weight of the mixture of manganese oxide particles and polyaniline.